Magnetic properties of chromium-doped Ni80Fe20 thin films

This paper investigates the properties of thin films of chromium-doped Ni80Fe20 (Permalloy) that could potentially be useful in future low-power magnetic memory technologies. The addition of chromium reduces the saturation magnetization, Ms, which is useful for low-energy switching, but does not significantly degrade the excellent switching properties of the host material even down to 10 K, the lowest temperature measured, in films as thin as 2.5 nm. As an example, an alloy film composed of 15% chromium and 85% Ni80Fe20 has an Ms just over half that of pure Ni80Fe20, with a coercivity H-c less than 4 Oe, an anisotropy field H-k less than 1 Oe, and an easy-axis remanent squareness M-r/M-s of 0.9 (where M-r is the remanent magnetization). Magnetodynamical measurements using a pulsed inductive microwave magnetometer showed that the average Landau Lifshitz damping lambda was relatively constant with changing Cr content, but increased significantly for thinner films (lambda approximate to 150 MHz for 11 nm, lambda approximate to 250 MHz for 2.5 nm), and at low bias fields likely due to increased magnetic dispersion. Density functional theory calculations show that chromium reduces M-s by entering the lattice antiferromagnetically; it also increases scattering in the majority spin channel, while adding almost insignificant scattering to the minority channel. (C) 2018 The Authors. Published by Elsevier B.V.